1. Field of Invention
The present invention relates to a method for the confinement of gun propellants during the initial stage of ignition, especially in small volume igniters. The invention allows temporary confinement of an initial small volume of liquid propellant up to a pressure of several thousand pounds per square inch. After robust ignition has taken place, the confinement is removed by the thermal energy released by the combustion, and the hot gases and burning propellant are released into a larger volume to ignite the propellant therein. This larger volume may be either the main charge of an intermediate ignition stage or the main propellant charge.
2. Discussion of the Prior Art
The liquid propellant which is proposed for gun applications has a characteristic which is similar to many other propellants. Such a propellant requires pressures substantially above ambient atmospheric pressure to achieve complete ignition. Guns using liquid propellants have previously addressed this problem by igniting a small volume (typically less than one milliliter) completely filled with propellant. The propellant self-pressurizes due to the start of decomposition and heating when energy is deposited into the propellant because it is confined in the chamber with only limited pressure relief through either a small diameter exit orifice or a long, narrow exit tube of somewhat larger diameter. Although previous studies have centered primarily on electrical ignition, and the present device has been demonstrated using laser ignition, the confinement requirement is present and probably similar in both cases.
In a prior art method, a small diameter, short length-to-diameter ratio orifice venting is based on the pioneering work of Felix Weinberg and his co-workers [for example, Carleton, et al., "Plasma Propellant Jet Ignition," 21st Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, p. 1885, 1988]. This approach was modified by engineers in application to actual gun propellant because they found that the small orifice was too confining once ignition had taken place. They then developed a long tube "inertial" confinement which confines the propellant by using a length-to-diameter tube as the exit. This tube is initially filled with liquid at the same time as the small chamber; the inertia and viscosity of this liquid in the tube confines the material in the igniter section for a short period of time to allow for the required high pressurization. (for example, FIG. 1 in DeSpirito, et al., "Electrical Ignition of LGP 1856 in a Two-Stage Ignition," BRL Memorandum Report BRL-MR-3748, 1989).
However, the use of the long tube as an exit orifice in the second device described (DeSoirito, et al.) results in significant heat loss to the tube walls as well as the destruction of many of the highly reactive combustion species (radicals) that are the basis of the efficiency of Weinberg's device.